Generally, to stabilize an output voltage of a Switching Mode Power Supply (SMPS), the related art disposes an error detection circuit in an output voltage switching unit of a trans unit, detects an error of an output voltage with the error detection circuit, and feeds back the detected error voltage to a power change unit through an opto coupler, thereby controlling the output voltage.
The trans unit changes a current to a current suitable for an Light Emitting Diode (LED) and supplies the changed current to the LED. As a device for regulating the current of the LED, an opto coupler is being used.